The invention relates to a device to be used as a tightening screw (for example, a nut) for tightening a rotary tool, such as the wheel of a hand grinder and circular saw or hand saw, to a mounting threaded part (for example, male threading) spirally provided in a drive shaft. The device is capable of powerful tightening with a small rotary input, and also of being loosened with relative ease. The device includes a means for regulating excessive tightening.
To mount a rotary tool such as a grinding wheel and circular saw on a driving shaft, hitherto, a flange and male threads were formed at the end portion of the driving shaft, and the rotary tool was fitted to the male threaded part, and a tightening screw with female threads (such as a nut) was fitted on its outer part, and by tightening the nut, the rotary tool was fixed between the nut and the flange.
In tightening and loosening operations of such a nut, however, a power tool such as a wrench was generally used, and therefore a sufficient amplification may not be obtained because only this power tool is used for amplifying the force to tighten or loosen the nut.
Besides, in the use of such a rotary tool, if the rotary tool is used with an impact, the nut may be tightened more than desired by the impact and its reaction, and it may not be removed by such power tool as a wrench. In this case the nut cannot be removed unless the rotary tool is broken in an extreme case.